In that case, then most people are idiots in your opinion.
Are you sure it's just a tape seal?
You forgot all about the screen. Look at step 5 of the iFixit teardown: http://www.ifixit.com/Teardown/iMac+Intel+21.5-Inch+EMC+2544+Teardown/11936
What about the screen? It's attached to the glass and comes off in one piece.
Let's face it; you fall into the paranoid idiot category.
It's a simple and easy upgrade. As stated, the Genius Bar techs are no smarter than the average repair guy. Buy the replacement two way tape and it's a simple process.